SOHC vs. DOHC....which gets more MPG?

[Zesty]

OK, sorry if this has been covered, I'm just curious.

I know the SOHC is less powerful, but I am wondering which gets better fuel efficiency.

Is it the same/comparable? Or does one have the edge over the other? Thanks.

[EchoOfSilence]

DOHC by a little

[Zesty]

Thanks for the quick response.

[neverlift]

kade better dual cams=more power=less throttle=less$ on gas

[EchoOfSilence]

that's not even the reason.
it's just a little more efficient

[wootwoot]

efficent in what sense?
Just trying to understand =)

[BigVinnie]

Originally Posted by wootwoot

efficent in what sense?
Just trying to understand =)

1.) additional exhaust valve per cylinder adds for better flow, and scavaging.Creates larger curtain space and overall larger exhaust diameter, it helps to increase power and momentum(inertia). 16valve VS. 12valve, obviously in this instance more is better.
2.) higher compression than the SOHC provides greater use of power for optimizing the atomization of air to fuel. More power by compressing more air than a lower compression engine.
3.) 8bit mapped ecu tuning over 16 bit ecu tuning. UUUMMMM obviously 16bit utilizes better maps, and much more aggressive tuning than the old 8bitters.
4.) DOHC heads are ported larger in diameter than the SOHC's.

The only true disadvantage to the DOHC's is the knock sensor, using lower grade fuels lower than 91 octane can actually hurt and decrease gas mileage by retarding the timing to impending knock signals that would read higher than using a higher grade (91 octane). Sohcs you can use the crappy 87 octane and get the same gas mileage results as if you were to use 91 octane on the SOHC's.....

[EchoOfSilence]

how does one more valve increase scavenging, vinnie?

[BigVinnie]

Originally Posted by EchoOfSilence

how does one more valve increase scavenging, vinnie?

Diameter size is increased due to curtain space area. It makes stronger pulses than utilizing a single exhaust valve....
More area=more volume
more volume=stronger pulse

[Irukandji]

My sohc got 250-270 on a full tank
My dohc gets 300-350 on a full tank

I'm not trying to say my cars were prime examples to show mpg... but my Dohc gets suprisingly better gas mileage.

[sunnys14]

dohc wastes gas TWICE as much as sohc because it has an extra cam

[2forty]

iono, my sohc and dohc got similar mileage, but sohcs usually do worse because of bad conditions haha

[sunnys14]

i think ur wrong 2forty

[sunnys14]

im jk, 2forty is right though, DOHC i see get a couple more MPG than SOHCs

[EchoOfSilence]

Originally Posted by n1sm0r

My sohc got 250-270 on a full tank
My dohc gets 300-350 on a full tank

I'm not trying to say my cars were prime examples to show mpg... but my Dohc gets suprisingly better gas mileage.

pretty much. I fucking hate getting 250-270 a tank, while Evan's (nemeguero) dohc gets above 330 (when he was N/A). damnit.

[breakindrifts]

Originally Posted by sunnys14

dohc wastes gas TWICE as much as sohc because it has an extra cam

sig worthy, but yea I can get around 300 miles to the tank on my sohc if I drive right.

[NIK90s13]

I'm in the 250/270 catagory. We just finished the dohc rebuild with the 91 exaust cam on the intake side. I just dont have the time to install it AAAAHHHHH!!!! It should go in in 2 weeks!!!!!

[Zesty]

Man, thanks for all the feedback. Pretty throughly answered my question!

So the DOHC is not as keen on the piss-gas as the SOHC is?

[BigVinnie]

Originally Posted by Zesty

So the DOHC is not as keen on the piss-gas as the SOHC is?

Yeah pretty much the only advantage the SOHC has over DOHC.
When ever lower grade fuels are used on the DOHC, cylinder temprature increases . As temprature increases from lower grade fuels, the knock sensor picks up knock (which is early signs of detonation). The knock sensor sends the signal to the ECU that the engine timing needs to be retarded in order to prevent early detonation. Retarding the timing decreases power output when the engine should of made optimal power at 20BTDC.
But even if the DOHC ran on crappier fuel it would still get better gas mileage than the SOHC. There are to many updated modifications to the DOHC engine that make it overall a better performer. The DOHC engine would probably lose about 1/2 mile per gallon using 89octane, and about 3/4mile per gallon using 87 octane, (or atleast this is what I figured going on long road trips and opening up the throttle). WOT also has alot to do with how much fuel is used. If you can keep the engine at or below 3000RPM you can pretty much use any grade fuel without sacrificing to much knock or gas mileage on crappier fuels. It is recomended for best performance to miles per gallon to use 91 octane on the DOHC engines.
But even on crappier fuels DOHC>SOHC.

[sunnys14]

Originally Posted by breakindrifts

sig worthy, but yea I can get around 300 miles to the tank on my sohc if I drive right.

it was just a joke

[sunnys14]

the most ive ever hit was 425miles on a s14 DOHC, bone stock. refilled with 16 gallons of 89 octane, so u can pretty much do the math.

(btw, the s14 has a huge gas tank, like 17gallons)

[BigVinnie]

Originally Posted by sunnys14

the most ive ever hit was 425miles on a s14 DOHC, bone stock. refilled with 16 gallons of 89 octane, so u can pretty much do the math.

(btw, the s14 has a huge gas tank, like 17gallons)

16Gallons eeh and 425 miles????? How did you calculate anything so relative???

[Irukandji]

the most i've ever seen was 380 on a tank... 425 is crazy.

[EchoOfSilence]

i have to call it...

[BigVinnie]

Originally Posted by EchoOfSilence

i have to call it...

HAHA....Agreed someone is smoking too many trees..........

[Ricks15]

I guess all engines are different in the condition that there in anb the abuse they take from us I remember when i was running rich and full of engine problems a Full tank would only last 80miles, and this isnt bs People with SOHC kae's gota know exactly what im talking about.

[alienz]

hey my sohc has gotten 400 miles to the tank but im sure the dohc can get more...just depends on your driving. ive literally gotten 400 miles a tank then turned around and gotten 200 miles then did 400 again and back to 200...but its not fun driving trying to get 400 miles to the tank. must constantly fight urges and retards trying to run you!

[BigVinnie]

I am still going to have to disagree. Weither it is SOHC or DOHC the bore and stroke of the engine leads to MASSIVE fuel dumping till about 1200RPM just to build enough power. Even if you did stay within 3000RPM and shifted properly on the standard s13 and s14 gas tanks that are offered, you will relatively get between the 300~350 at the maximum (weither SOHC or DOHC and how you drive). It is all supported by the EPA which has done alot of testing on all of these cars before approved for sale in the U.S.
Kinda makes you wonder the conspiracy of hybrid cars though doesn't it.
Anyways to get back on point we don't drive small bore and stroke Honda's that could probably conserve fuel a little bit better. We drive big bore and stroke engines that aren't very conservative when it comes to making torque.

[Pacman]

Doesn't the hemispherical combustion chamber of the DOHC get any credit for better MPG? I know the burn patter for a Hemispherical chamber is better then the others.

[ranisron]

S13 Fuel Tank, KA24DE, 15.9 Gallon, the best mileage I have gotten was 32 mpg to the gallon on 89 octane gas.

U13 (Altima) fuel tank, KA24DE (hello, same engine), 15.9 Gallon, the best mileage I have gotten was 35 mpg, 89 Octane (I have no idea how I did it).

Both cars run on 205 series tires, with the 240SX being lighter and healthier (I think). 240SX has higher tire pressures, which should results in better gas mileage. but I was getting some premature brake engagement so it tends to fuck things up.

Driving was done on the same highway, I-70, from Martinsville, IN to Cambridge, OH, which is about 28X.00 miles.